Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session H11: MeV Gamma Ray Astronomy and Astroplasma Processes |
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Sponsoring Units: DAP Chair: James Ryan, University of New Hampshire Room: Hyatt Regency Jacksonville Riverfront City Terrace 7 |
Sunday, April 15, 2007 8:30AM - 8:42AM |
H11.00001: Thermal and Nonthermal Radiation in SNRs from Efficient Shock Acceleration Don Ellison, Daniel Patnaude, Patrick Slane Efficient cosmic ray acceleration in supernova remnants results in~both higher shock compression and lower post shock temperatures compared to cases where cosmic ray production is ignored. These changes in the properties of the shocked plasma will translate into changes in the thermal X-ray emission in the interaction region between the forward and reverse shocks. Furthermore, the relativistic cosmic ray electrons produced in the diffusive shock acceleration process generate nonthermal X-ray synchrotron emission which is self-consistently determined with the thermal emission through the nonlinear shock acceleration mechanism. We present results from simulations where the remnant hydrodynamics are coupled to efficient cosmic ray acceleration and to a nonequilibrium ionization calculation of thermal X-ray emission. By~varying the particle injection efficiency, ambient density, and the~electron heating mechanism, we produce a grid of models which show~variations~in~the~resultant~X-ray spectra where the thermal and nonthermal contributions are determined self-consistently. [Preview Abstract] |
Sunday, April 15, 2007 8:42AM - 8:54AM |
H11.00002: Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification Andrey Vladimirov, Don Ellison, Andrei Bykov Recent observations suggest the presence of large magnetic fields in supernova remnants (SNRs), and a likely explanation of these fields is generation of MHD turbulence by shock-accelerated particles. We present a Monte Carlo model of nonlinear diffusive shock acceleration allowing for the production of large-amplitude magnetic turbulence and show preliminary results where the ambient field is amplified by large factors. In addition, we investigate the influence of the dissipation of the turbulence on the flow of plasma and on the injection of thermal particles into acceleration process. This model is the first to include strong wave generation and dissipation, efficient particle acceleration to relativistic energies in nonrelativistic shocks, and thermal particle injection in an internally self-consistent manner. The generation of large magnetic fields in SNRs will strongly influence the production of relativistic ions and electrons and impact broad-band photon observations, particularly the mixture of inverse-Compton and pion-decay emission in the GeV-TeV energy range relevant for GLAST and air-Cherenkov telescopes such as HESS, Veritas and MAGIC. [Preview Abstract] |
Sunday, April 15, 2007 8:54AM - 9:06AM |
H11.00003: Broken Symmetry and Coherent Structure in MHD Turbulence John Shebalin Absolute equilibrium ensemble theory for ideal homogeneous magnetohydrodynamic (MHD) turbulence is fairly well developed [1]. Theory and simulation indicate that ideal MHD turbulence is non-ergodic and contains coherent structure. The question of applicability to real ({\it i.e.}, dissipative) MHD turbulence is examined. Results from several very long time numerical simulations on a $64^3$ grid are presented. It is seen that coherent structure begins to form before decay dominates over nonlinearity. The connection with inverse spectral cascades and selective decay will also be discussed.\\ \mbox{[1]} J. V. Shebalin, {\it J.\ Plasma Phys.}, {\bf 72}, 507-524, 2006. [Preview Abstract] |
Sunday, April 15, 2007 9:06AM - 9:18AM |
H11.00004: New Arecibo-DRAO deep probe of magnetized plasma in a supercluster environment Philipp Kronberg, Roland Kothes, Christopher Salter, Phil Perillat Using the first combination of the world's largest radio telescope at Arecibo, and the precision-imaging DRAO Interferometer at Penticton BC, we present a deep, wide field (over 50 sq. degrees) search for faint, 0.4 GHz synchrotron emission at unprecedented low surface brightness levels on scales from 3' to 8 degrees. I describe several new results that emerge: (1) A 2 - 3 Mpc - sized zone of intergalactic magneto- plasma is magnetized at levels B $>$ 0.1 microgauss, (2) A striking lack of global correlation between zones of faint synchrotron radiation and baryonic matter (i.e. star \& galaxy) overdensity in the local universe, (3) supporting evidence for magnetic and CR energy release from massive galaxy black holes into wider intergalactic space, (4) the first detailed view of foreground Galactic and extragalactic features that might contribute to CMB backgrounds on scales to be imaged by the PLANCK CMB explorer, and (5) constraints on the distributed acceleration and diffusion of CR's in intergalactic space. [Preview Abstract] |
Sunday, April 15, 2007 9:18AM - 9:30AM |
H11.00005: ABSTRACT WITHDRAWN |
Sunday, April 15, 2007 9:30AM - 9:45AM |
H11.00006: Positron Annihilation in the Galaxy: Spatial Distribution and Spectral Characteristics Georg Weidenspointner, Juergen Knoedlseder, Pierre Jean, Gerry Skinner, Jean-Pierre Roques, Peter Milne, Roland Diehl The imaging spectrometer SPI on board ESA's INTEGRAL observatory provides us with an unprecedented view of positrons in our Galaxy.The first all-sky maps in the 511~keV annihilation line and in the positronium continuum showed a puzzling concentration of annihilation radiation in the Galactic bulge. Fine spectroscopy of the bulge emission indicated that the positrons annihilate in the warm interstellar medium. By now, about twice as many INTEGRAL observations are available, allowing us to study the detailed spatial and spectral characteristics of the dominant emission from the Galactic center region and to investigate the faint disk emission. In addition, for the first time we obtain intriguing evidence for extended, low surface brightness emission from regions outside the bulge and the stellar disk. These spatial characteristics are unlike those of any known Galactic population and emphasize the importance of understanding the propagation of positrons when relating the observed sky distribution of 511~keV line emission to the Galactic distribution of potential positron sources. [Preview Abstract] |
Sunday, April 15, 2007 9:45AM - 10:00AM |
H11.00007: Nucleosynthesis in the Galaxy as seen in diffuse radioactivity gamma-rays ($^{26}$Al, $^{60}$Fe) Roland Diehl Four mission years of INTEGRAL have led to discoveries of new sources and to detailed astronomical refinements of already-known gamma-ray line emission. Recent massive-star nucleosynthesis is traced throughout the Galaxy with radioactivites seen in $^{26}$Al and now also $^{60}$Fe gamma-rays. Precision line spectroscopy reveals Doppler shifts for the $^{26}$Al line, separately for different parts of the Galaxy. This provides new insights into the dynamics of hot interstellar gas, especially in inner-Galaxy regions which are otherwise difficult to observe. The processes generating new atomic nuclei in stars and supernovae are reflected in the abundances of these ejected radioactivities. We will discuss the recent spectroscopic information on these gamma-ray lines and their broader implications, in terms of massive-star nucleosynthesis models and Galactic massive-star content with its nucleosynthesis activity. [Preview Abstract] |
Sunday, April 15, 2007 10:00AM - 10:15AM |
H11.00008: High-energy Emission from Accreting Binaries: Constraints with SPI/INTEGRAL J.P. Roques |
Sunday, April 15, 2007 10:15AM - 10:30AM |
H11.00009: Hard X-ray Emission from AGN and the Cosmic X-ray Background (CXB) Volker Beckmann, Neil Gehrels, Simona Soldi The CXB is believed to be caused by unresolved X-ray sources, and peaks around 30 keV. While the CXB below 20 keV is well understood, no all-sky survey has been available at the peak of the CXB before the INTEGRAL mission. Up to now more than 130 AGN have been detected by INTEGRAL above 20 keV. INTEGRAL can contribute to our understanding of the AGN phenomenon mainly in two ways. By deriving high signal to noise spectra up to several hundred keV to study the physical processes involved in this energy range, such as Compton reflection. And by looking at the statistical properties of AGN seen by INTEGRAL, one can study the contribution to the CXB and the role of heavily absorbed type II AGNs We have compiled a complete extragalactic sample based on $\sim 25,000$ square degrees in the 20-40 keV band with INTEGRAL and present the first luminosity function of AGN in this energy range. The objects explaining the peak in the cosmic X-ray background are likely to be either low luminosity AGN ($L_X < 10^{41} \rm \, ergs \, s^{-1}$) or of other type, such as intermediate mass black holes, clusters, and star forming regions. An alternative scenario is an evolution of the source population, with an increasing fraction of absorbed sources with redshift. [Preview Abstract] |
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